Magnetic excitations and phonons simultaneously studied by resonant inelastic x-ray scattering in optimally doped Bi_(1.5)Pb_(0.55)Sr_(1.6)La_(0.4)CuO_(6+δ)

摘要

Magnetic excitations in the optimally doped high-T_c superconductor Bi_(1.5)Pb_(0.55)Sr_(1.6)La_(0.4)CuO_(6+δ) (OP-Bi2201, T_c ≃ 34 K) are investigated by Cu L_3 edge resonant inelastic x-ray scattering (RIXS), below and above the pseudogap opening temperature. At both temperatures the broad spectral distribution disperses along the (1,0) direction up to ～350 meV at zone boundary, similar to other hole-doped cuprates. However, above ～0.22 reciprocal lattice units, we observe a concurrent intensity decrease for magnetic excitations and quasielastic signals with weak temperature dependence. This anomaly seems to indicate a coupling between magnetic, lattice, and charge modes in this compound. We also compare the magnetic excitation spectra near the antinodal zone boundary in the single layer OP-Bi_2201 and in the bilayer optimally doped Bi_(1.5)Pb_(0.6)Sr_(1.54)CaCu_2O_(8+δ) (OP-Bi2212, T_c ≃ 96 K). The strong similarities in the paramagnon dispersion and in their energy at zone boundary indicate that the strength of the superexchange interaction and the short-range magnetic correlation cannot be directly related to T_c, not even within the same family of cuprates.